Some of the cognitive symptoms of schizophrenia have been attributed to dysfunction of the dorsal prefrontal cortex (dPFC), and this dysfunction appears to be associated with alterations of the neural circuitry within the dPFC and in its connections with the mediodorsal nucleus (MDN) of the thalamus. In the dPFC, these alterations include disturbances in markers of GABA neurotransmission that are restricted to a subset of GABA neurons. The studies proposed in this application are designed to identify the affected subset of GABA neurons, to define the postsynaptic consequences of the alterations in these neurons, and to characterize the pathophysiological mechanisms that may produce these alterations. Specifically, we plan to test the following hypotheses: 1) The affected subset of dPFC GABA neurons in schizophrenia is composed principally of the chandelier and wide arbor subclasses, which are specialized for potent inhibitory control over cortical pyramidal neuron activity. 2) The disturbances in these GABA neurons are accompanied by changes in the GABA-A receptor subunit proteins that are postsynaptic to the axon terminals of chandelier and wide arbor neurons. 3) In the dPFC of subjects with schizophrenia, the expression pattern of genes involved in GABA neurotransmission is consistent with alterations in chandelier and wide arbor neuron connectivity. 4) These changes in pre- and postsynaptic markers of GABA neurotransmission are specific to the pathophysiology of schizophrenia. 5) Altered GABA markers are not restricted to the dPFC in schizophrenia, but are also found in other cortical regions that receive input from the MDN. 6) Experimental lesions of MDN neurons in macaque monkeys produce changes in dPFC GABA neurons similar to those seen in schizophrenia. The power of the proposed studies derives from an integration of molecular and anatomical approaches, in both humans and nonhuman primates to test hypotheses regarding the circuit-specificity and underlying causes of altered dPFC GABA neurotransmission in schizophrenia. Together, these studies will provide a comprehensive molecular-and circuit-based accounting of the contribution of abnormalities in GABA neurotransmission to dPFC dysfunction in schizophrenia.